In accordance with development of mobile communication, optical communication and satellite communication and popularization of mobile phones, producing of RF devices for processing RF signal such as filter, duplexer and waveguide is being increased.
In processing high frequency RF signal such as microwave, Skin effect occurs that high frequency current becomes maximized on surface layer. In order to obtain desired characteristic in desired frequency band, alternating current loss should be reduced. In order to reduce loss, plating process is performed, and silver plating is generally performed.
It is known that surface roughness and plating method affects alternating current loss. In order to reduce loss, proper plating method should be used corresponding to shape of the device and proper plating solution should be selected.
Further, by proper plating treatment, throwing power and surface roughness should be improved and adhesion should also be improved while reducing electronic resistance.
On the other side, the thickness of plating layer is associated with the skin effect in high frequency, the skin depth by the skin effect can be expressed by following equation 1.
                    1                              π            ⁢                                                  ⁢            f            ⁢                                                  ⁢            μσ                                              [                  Equation          ⁢                                          ⁢          1                ]            
In equation 1, π is constant, μ is magnetic permeability, f is frequency and σ is conductivity.
Among various RF devices on which silver plating is performed, in case of RF cavity filter, the silver plating was performed after basic structure of which the material is aluminum or aluminum alloy was manufactured. Generally, basic structure is manufactured through mold and the silver plating is performed by digesting the basic structure in plating solution in order to manufacture RF device.
As described above, when the basic structure of aluminum material is manufactured and then silver plating is performed, weight of the RF device becomes heavier and the silver plating is performed on unnecessary part such as exterior part. Silver plating layer of exterior part was main cause of corrosion and discoloration when the RF device is used for a long time.
In another conventional method for manufacturing the RF device, basic structure was made of plastic material and then silver plating was performed on the plastic material basic structure.
When the silver plating is performed on plastic material, weight of the RF device is may be lighter. However, plating method becomes more complex than case that silver plating is performed on metal. Further, although silver plating is performed on the plastic material, silver plating was still performed on unnecessary part such as exterior part of the RF device. Furthermore, depreciation by heat such as wrench by heat was more serious when plastic is used.